Additionally, it was suggested during editing (though I did leave it out) that I talk about the mere-exposure effect, where people like what's familiar.

A full understanding of all the factors going into self-perception would include things which contribute to AND detract from a positive self-perception, with mere-exposure and other effects biasing the answer up, and excessive attention to flaws and probably other phenomena biasing the answer down.

I might imagine we end up with a "net" self-perception, an amalgamation of all the effects. For some people, that net perception might be biased up. Indeed, while I'm very hesitant to draw too many conclusions from the study you provide from the 1800's, it is POSSIBLE that the majority of people have a net self-perception biased up.

Still leaving millions of people, several of whom I know, who could benefit from the ideas in this article, I think.

And if I had to guess, in 1878, people, on average, were probably more satisfied with their appearance than we are now.